This invention relates to signal detectors. More particularly, this invention relates to providing dynamically adjustable signal detectors for programmable logic resources.
Programmable logic resource technology is well known for its ability to allow a common hardware design (embodied in an integrated circuit) to be programmed to meet the needs of many different applications. Known examples of programmable logic resource technology include programmable logic devices (PLDs), complex programmable logic devices (CPLDs), and field programmable gate arrays (FPGAs).
Programmable logic resources typically include large numbers of regions of programmable logic and other resources such as memory, input/output circuits, etc., that are selectively interconnectable via programmable interconnection resources on the programmable logic resources. For example, each region of programmable logic on a programmable logic resource may be programmable to perform any of several relatively simple logic functions on several input signals applied to that region in order to produce one or more output signals indicative of the result of performing the selected logic function(s) on the input signals. The interconnection resources are programmable to convey signals to, from, and between the logic regions in any of a wide variety of patterns or configurations.
Programmable logic resources can be designed to support multiple signaling protocols. These signaling protocols vary with respect to such parameters as clock signal frequency, header configuration, packet size, data word length, number of parallel channels, etc. Such signaling protocols can include, for example, (1) industry-standard forms such as XAUI, InfiniBand (IB), Fibre Channel (FC), Gigabit Ethernet, Packet Over SONET or POS-5, Serial RapidIO, etc., and (2) any of a wide range of non-industry-standard or “custom” forms that particular users devise for their own uses. Such custom protocols often have at least some features similar to industry-standard protocols, but deviate from industry standards in other respects.
Differential signaling circuitry is often used to provide interconnection paths between transmitters and receivers in programmable logic resources. A transmitter includes a differential driver circuit for converting a single input signal to a pair of differential signals. Two conductors are used to convey the differential signals from the driver circuit to a receiver. The receiver includes a differential receiver circuit for converting the pair of differential signals back to a single signal for output to digital circuitry or analog circuitry.
A signal detector is often used in the differential receiver circuit to determine whether the differential signals being received from the transmitter are valid. To determine the validity of a differential signal, a differential input voltage (VID) is computed and compared to a minimum differential voltage (VMIN). The differential input voltage is a difference between the positive terminal and the negative terminal of the differential signal. The minimum differential voltage is a fixed value generally associated with a given signaling protocol. The differential signal is valid when the differential input voltage is greater than or equal to the minimum differential voltage (e.g., VID≧VMIN).
Because known signal detectors are designed to operate for a given signaling protocol, a signal detector cannot be changed in order to support a different signaling protocol. Furthermore, changes can occur in the link between the transmitter and the receiver that can result in the minimum differential voltage being less effective in determining whether a differential signal is valid. Such changes, which can be due to component aging or environmental conditions (e.g., changes in temperature or voltage), can be classified as minor or serious. A minor change to the link can cause the differential input voltage to no longer meets the minimum differential voltage. However, the receiver may be able to tolerate a smaller minimum differential voltage while continuing to allow the system to operate reliably. A major change to the link can cause the differential input voltage to change too often or can cause the minimum differential voltage to be too small to be effective in determining whether a differential signal is valid.
In view of the foregoing, it would be desirable to provide a dynamically adjustable signal detector that supports different signaling protocols and adapts to changes in the link between the transmitter and receiver.